Generally, various control circuits known as pump-off control circuits have been proposed, such as in my copending patent applications Ser. No. 331,804, filed Feb. 12, 1973 and Ser. No. 437,833, filed Jan. 30, 1974 to shut off the power to the pump drive motor when the supply of liquid in the well has been pumped dry to prevent damage to the equipment and the use of unnecessary power. Generally, such pump-off control circuits are initially actuated by a timer at periodic intervals, after which the control circuit is initiated, to control the power to the pump drive motor and shut off the power when the well has been pumped dry. The pump-off control circuit senses either the current or power drawn by the pumping unit and utilizes the fact that the power required by the pump drive motor is less when no liquid is being produced from the well than when liquid is being produced to turn off the pump drive motor.
The present invention is directed to a malfunction detector circuit which is used in conjunction with any suitable pump-off control circuit for example such as described in the foregoing applications, for providing an indication as to whether the pump-off control circuit is operating satisfactorily, and whether or not there are other abnormal conditions in the well which should be noted. The present malfunction detector monitors the current drawn by the drive motor and detects such malfunctions as parted rods, split tubing, worn pumps, stuck traveling valves or standing valves and other abnormal situations.